The mechanics, briefly#
P/B = market price per share ÷ book value per share, where book value per share is (total assets − total debts) ÷ shares outstanding.
Worked through: a company with $100M in assets and $40M in debt has a $60M book value. Across 10M shares that’s $6 per share. If the stock trades at $12, the P/B is 2 — investors are paying twice what the balance sheet says the company owns.
The standard interpretation follows:
- Below 1 — trading under book value. Possibly undervalued, possibly a warning.
- At 1 — market price matches book value.
- Above 1 — investors are paying a premium for expected growth.
Simple enough. The problem is that “what the company owns on paper” has become a smaller and smaller fraction of what companies are.
The accounting gap has swallowed the ratio#
Ocean Tomo’s long-running study of S&P 500 composition found that intangible assets now account for about 92% of index market value, leaving roughly 8% attributable to tangible assets.
The reversal is the striking part. In 1975 tangible assets made up 83% of S&P 500 market value and intangibles just 17%. That has completely inverted in fifty years.
Book value captures buildings, inventory, equipment and cash. It does not capture brand, software, intellectual property, network effects, customer relationships or recurring revenue — because accounting standards generally only record intangibles when they’re purchased, not when they’re built.
So a company that spent two decades building the most recognised brand in its category records essentially nothing for it, while a competitor that bought a comparable brand carries it as goodwill. Same economic asset, different book value, and P/B treats them as different companies.
Which is why the industry examples diverge so hard#
A tech company at P/B 10.5 isn’t expensive — its value is software, IP and brand, and virtually none of that is on the balance sheet. High P/B is the expected reading, not a warning.
A furniture manufacturer at P/B 0.7 has warehouses and inventory that the market has judged worth less than the accountants claim. Here the ratio is doing real work.
A bank at P/B 1.2 is the ratio’s natural home. Bank assets are cash and loans — tangible, marked, reliably valued. That’s why bank P/Bs cluster near 1 and why deviations from it are meaningful.
Coca-Cola’s P/B above 10 is the cleanest illustration. What you’re buying is a brand and a century of distribution, and book value can see neither.
The 2008 lesson: a low P/B can mean the books are wrong#
The most expensive misreading of this ratio happened in plain sight.
During the 2008 financial crisis, bank stocks fell to P/B ratios well below 1. On the standard interpretation these were obvious bargains — buy a dollar of assets for seventy cents.
The balance sheets were the problem. They carried mortgage-backed securities and structured products at values the market no longer believed. Lehman Brothers collapsed. Bank of America and Citigroup required government support.
The lesson generalises beyond banks: a low P/B can mean the market is right about the assets and the accountants aren’t. Book value is an accounting estimate of what things are worth, and estimates are made with assumptions. When the assumptions break, book value breaks first and the ratio flatters the stock right up to the failure.
The pattern is consistent enough to be a rule. A P/B below 1 in a sector where the ratio should work is either a genuine mispricing or a signal that someone’s asset valuations are stale. You have to determine which, and the ratio can’t tell you.
Where to actually use it#
Use it for banks, insurers, real estate and asset-heavy manufacturing — anywhere the balance sheet contains most of the business. In those sectors, a P/B meaningfully below peers is a question worth asking.
Don’t use it for technology, software, pharmaceutical research, consumer brands or anything where value lives in IP, reputation or recurring revenue. There the ratio isn’t wrong so much as uninformative; you’ll conclude every good company is expensive.
Always pair it. P/E, revenue growth, debt levels and cash flow. The figure is on Yahoo Finance under Statistics, which makes it easy to find and easy to over-rely on.
Summary — and what to do about it#
P/B compares price to the visible portion of a business. For most modern companies, the visible portion is a rounding error.
- Check the industry before you check the ratio. Asset-heavy, it’s informative; asset-light, it’s noise.
- Remember the 92%. Intangibles are most of modern market value and none of book value.
- Treat a P/B below 1 as a question about the assets. 2008’s banks were the demonstration.
- Expect high P/B from brand and IP businesses. Coca-Cola above 10 is the ratio failing, not the company being overpriced.
- Compare against sector peers, never across sectors. A bank at 1.2 and a software firm at 1.2 mean opposite things.
- Pair it with P/E, revenue growth, debt and cash flow. No single ratio survives alone.
The number is easy to find and easy to misread, which is a bad combination. It’s telling you about the part of a business you can weigh — and that’s rarely the part you’re buying.
Sources & further reading#
- Business Valuation Resources on Ocean Tomo’s study — intangibles at 92% of S&P 500 market value.
- Ocean Tomo Intangible Asset Market Value Study — the shift from 17% intangible in 1975 to 92% today.
- World Trademark Review on the same study — what book value systematically fails to record.
- Federal Reserve History, “The Great Recession” — context on the 2008 bank collapses and interventions.
